Modulated carrier wave transmitter



March 7, 1939. E. GREEN 2,149,432

MODULATED CARRIER WAVE TRANSMITTER I Filed Dc. 8, 1936 2 Sheets-Sheet l 50a/20E UFA/1000m r//VG Pare/vr/Azs CARR/ER WA VE .SOURCE 0F Vl. FSoz/ECE nivo {impur/Ee INVENTOR ERNEST GREEN l l l mpg/ ZM y 26 f u ATTORNEY March 7, 1939. E. GREEN 2,149,432

` MODULATED CARRIER WAVE TRANSMITTER Filed Dec. 8, 195e A2 sheets-sheet 2 JOI/RCE 0F MUDUM TNG PUTE/VTM LS A, Soz/RC5 0F f Mmmm/6 2) 6 PorfA/r/Azs ATTORNEY Patented Mar.. 7, 1939 UNITED STATES MODULATED CARRIER WAVE TRANSMITTER Ernest Green, Writtle, Chelmsford, England, as- Signor to Radio Corporation of America, a corporation of Delaware Application December 8, 1936,'.Serial No. v1111!,'1'35 In Great Britain January 8, 1936 6 Claims.

This inventionrelates to radio and other modulated carrier wave transmitters and more particularly to transmitters of the so-called series modulation kind, i. e., of the kind wherein modulation is effected by a tube or bank of tubes whose internal impedance or impedances forms part of a series circuit which also includes the internal impedance or impedances of a tube or bank of tubes (and their associated circuits) operating at the carrier frequency to be modulated.

According to the main feature of this invention the control grid Voltage applied to the grid or grids of the modulator tube or tubes of a transmitter of the kind referred to vincludes a unidirectional varying component which is derived by rectifying the modulated energy.

Though not limited to its application thereto, the main feature of this invention is especially suited forl application to a so-called floating carrier system as described in the specification of British Patent #427,026 accepted April 15, 1935.

According to a second feature of this invention the control grid voltage applied to the grid or grids of the modulator tube or tubes of a transmitter of the kind referred to includes a unidirectional substantially xed bias component derived from the main high tension supply which is utilized to supply potential across the series modulation circuit.

Preferably both features of this invention are employed together.

For the sake of convenience in the description which follows the carrier frequency tube or bank of tubes whose internal impedance or impedances together with associated circuits are,.

in a series modulation system, connected in series with the anode-cathode space or spaces of the modulating tube or bank-of tubes across the main high tension supply, will be referred to briefly as the load resistance. In practice, of course, this load resistance will generally be constituted by circuits including the anode-cathode space or spaces of a carrier frequency amplified tube or bank of tubes whose grid circuit input consists of the carrier frequency to be modulated.

The invention is illustrated in the accompanying drawings which, in Figures 1 to 5 inclusive, show diagrammatically several embodiments of my modulation circuit, while Figure la shows a detail of the circuits of the other figures.

Referring rst to Figure 1 which shows one way of carrying out the rst feature of this invention, the load resistance which in this case is the modulated stage, represented at R is connected at one end to the positive terminal -l-HT of the main high tension supply and at the other to the anode of a modulator tube M whose cathode is connected to earth and also to the negative terminal of the said main high tension supply. The grid circuit of the modulating tube includes three 5 resistances R1, R2 and R3 in series. Modulating potentials from any suitable source, represented at G, are applied across the resistance R1 nearest the grid. A suitable xed bias potential V2 from a source lll is applied across the second resistance 10 R2; and the third resistance R3 is connected through a choke L which may be replaced by a resistance or other smoother element, across the output leads from a full wave rectier network. The resistances Rz, R3 are shunted by by-pass '15 condensers C2, C3 respectively. The full wave rectifier network includes a transformer T having a center-tapped secondary in series with two reotiers S which may be of the copper oxide type, the center tap of the secondary winding of 2O transformer T and the junction point of the two rectiflers S constituting the output leads from the network. The primary winding of the transformer T is connected in series with a suitable condenser C between the anode and cathode of 25 the modulator tube M. With this arrangement a component of bias V1 derived via the rectifier network by rectifying modulated carrier energy will be applied across resistance R3.

In a modfiication illustrated in Figure 2 the 30 load resistance R in series with the modulator tube M is on the negative side thereof, that is, is between the cathode and earth, instead of on the positive side thereof, that is, betweenits anode and the positive high tension terminal, as in Figure 1, and the primary winding of the transformer T, with its series condenser C is connected across the load resistance R instead of across the modulator tube M. As before the fixed bias potential V2 may be obtained from a 40 separate source l0.

It is preferred, however, as shown in the fur- -ther embodiment of Figure 3 to obtain the bias V2 from the main high tension supply by connecting a suitable high` resistance R5 between the negative terminal of the high tension supply source (earth) and the junction point of the resistances R1 and R2. If desired, and again as shown yin Figure 3, a variable resistance R4 may also be connected in series with the primary winding of the transformer T, while also, if desired, the choke L may be replaced by a .resistance Re (Figure 3). In AFigure 3 'essential elements of the modulated stage represented by R in the prior figures have been shown. This modulated stage may comprise an electron discharge device 20 having its anode 22 connected to the cathode of M and its cathode 25 connected by way of a radio frequency choke coil to ground as shown so that the primary winding of transformer T is in parallel with the impedance between the electrodes 22 and 25 of tube 20. A high frequency circuit is connected as shown by blocking condensers BC between the anode and cathode of tube 20 in conventional fashion. A high frequency source is connected as shown in Figure la between the control grid 24 and cathode 25 in the conventional manner.

The modulated stage shown inFigure 3 may beV used also in Figures 1, 2, 4, and 5 to replace R or as pointed out hereinafter a modulated stage as shown in Figure 1a may be used inall of the figures. Y Y

In a further embodiment shown in Figure. 4 there are two modulator tubes M1, M2 having their anodes connected togetherV and also their cathodes connected together. The anodes of the tubes M1, M2 are connected to the positive high tension terminal HT-iand the cathodes are connected to earth and'to the negative high tension terminal through the load resistance R. The modulator tube gridsV are connected as shown each to an adjustable tapping point upon a different one of two resistances RI', Ri. These resistances are connected at their upper ends' each through a'coupling condenser to one terminal of the modulating potential source at' G the lower ends of the said resistances being adjustably apped upon a resistance R2 one end of which is connected to earth through a high resistance R5 and the other end Yof which isr connected through a further resistance R3 to the cathode point. Suitable by-passing and ltering condensers Cc', C2 and' C3 are provided as shown. The junction point of resistances R2, R3 is connected through a choke or otherV smoothing element, such as a resistance Re, to one output load of a full wave rectifier network T, S, the other output lead of Y which is connected to the modulator tube cathode point.

The full wave rectifier network is as in the previous embodiments and the primary of the transformer T therein is connected in series with a condenser C across the loadv resistance R. The remaining terminal of the modulating potential source at G is connected to the tapping point Yat which resistance R1 is connected to resistance R2. l

In Figures l and 2, Vz'is provided from an eX- ternal insulated source, the negative terminal being towards the tube grid. In the absence of modulation this backs oi M to a low feed value. When modulation is applied, the rectiers S provide a voltage V1 across Ra in opposition to V2.

VThis reduces the resultant negative bias. on M and allows the feed toincrease.

In Figures 3 and 4 the xed bias of M is obtained fromY the current owing through R3, R, and then R5.

This variable bias due to modulation is provided by S across R3 and must be suicient toV overcome the increase of steady bias due to the increase of feed through M, R3 and R2.

Figure 5l shows a preferred embodiment of the seco-nd feature of this invention. Here the grid circuit of a modulator tube M, which is in series with the load resistance R across the high tension supply and is on the positive side, contains in series with a resistance R1 across which modulating potentials from G are applied, a further resistance R2 which is shunted by a condenser C2 trodes `connected as shown in Figure la.

of sufficient magnitude to by-pass all modulating frequencies. The junction point of resistances R1, R2 is connected through another resistance R5 to the earthed or negative supply terminal end of the load resistance R. The resistances R2 and R5 are of large value and take a very small fraction of the main current, being chosen of such value as to give the desired value of negative bias at the grid of the modulator tube. p

The impedance R of each of Figures 1, 2, 4, and 5 includes the impedance of a tube 20 having elec- In other words, the circuits and tube of Figure la may Vreplace the rectangle R in each of the other iiguresof the drawings. lIhis is accomplished by breaking the leads to R at points 26 and Z8 Vof the 4 `energy to be modulated is caused to flow and having output electrodes connected in a series modulation circuit wtih a modulating tube having electrodes onV which modulating potentials are impressed, both being connected with av source of direct current potential, to accomplish modulation of said wave energy by said modulating potentials, means for impressing a direct current biasing potential on a controlling electrode of said modulating tube, an impedance for impressing an additional controlling potential on a controlling electrode of said modulating tube which varies iny accordance with the modulationsV on said wave energy, and rectifying means coupling electrodes of saiddischarge tube to said impedance toimpress thereon additional controlling potentials to control the bias of said modulating tube in accordance with the modulations on said wave energy. l

2. In a modulation system., a Vdischarge tube stage having electrodes connected in an alternating'current circuit in which wave energy to be modulated is caused to ow and having output electrodes, aA modulating tube having electrodes on which modulating -potentials are impressed andr having'output electrodes, a source of direct current potential, means connecting the output electrodesfof said discharge tube and said modulating tube in series across said source of direct current potential, resistive means connected with said direct current source and a controlling electrode of said modulating tube for impressing a direct current biasing potentialV on said electrode Y of saidmodulating tube, a second resistive means connected with said last named resistive means for impressing a variable controlling bias on said last named electrode, a rectifier having input electrodes coupled with electrodesV of said discharge tube stage tol derive-therefrom modulated wave energy and rectifying the same to derive a component characteristic of the Ymodulations onsaid modulated wave energy, and a circuit connecting the output electrodes of said rectiiier to said second resistive means to impress thereon additional controlling potentials to control the bias of said modulatingtube in accordance with vthe modulations on said wave energy.

3. In a modulation system, a carrier frequency tube having electrodes on which wave energy to be modulated may be set up, a modulator tube having input electrodes on which modulating potentials may be impressed and having output electrodes, a source of direct current potential, means connecting the impedances between electrodes of said first tube and between the output electrodes of said modulating tube in series and to said source of direct current potential, resistive means for impressing a direct current biasing potention, on a controlling electrode of said modulator tube, a second resistive means connected with said last named resistive means, a rectifier having input electrodes coupled with electrode of said carrier frequency tube to derive therefrom modulated energy and a circuit connecting the output electrodes of said rectifier to said second resistive means to impress thereon additional controlling potentials to control the bias of the modulator' tube in accordance with the modulations in the output circuit of said carrier frequency tube.

4. In a modulation system a carrier frequency tube having electrodes connected in circuits in which wave energy to be modulated may be set up and having output electrodes, a modulator tube having a control grid and cathods connected with a source of modulating potentials and having output electrodes, a source of direct current potential, a circuit connecting the output electrodes of both of said tubes .and said source of direct current potential in a series modulation circuit, a plurality of resistances in series between the control grid and cathode of said modulator tube, means for impressing a direct current potential on one of said resistances to bias the control grid of said modulator tube relative to the cathode by a fixed amount, and means for applying additional biasing potential to another of said resistances to additionally control the bias on the control grid of said modulator tube by an amount which varies as the modulations on the wave energy vary, comprising a rectier having input electrodes coupled to electrodes of said carrier frequency tube, said rectifier having output electrodes coupled to said other of said flrst named resistances.

5. In a modulation system a carrier frequency tube having electrodes in circuits in which wave energy to be modulated is caused to flow and having output electrodes, a modulator tube having a control grid and cathode connected with a source oi modulating potentials and having output electrodes, a source of direct current potential, a circuit connecting the output electrodes of said tubes and said source of direct current potential in a series modulation circuit, the output electrodes of said modulator tube being in the high potential side of said series modulation circuit, a plurality of resistances in series between the control grid and cathode of said modulator tube, means for impressing a direct current potential derived from said source of direct current potential on one of said resistances to bias the control grid of said modulator tube relative to the cathode by a fixed amount, and means for applying additional biasing potential to another of said resistances to additionally control the bias on the control grid of said modulator tube an amount which varies in accordance with the modulations on said wave energy comprising a rectifier having input electrodes coupled to electrodes of said carrier frequency tube, said rectifier having output electrodes coupled to said other of said first named resistances.

6. In a modulation system of the type wherein a discharge tube stage has electrodes connected in a circuit in which wave energy to be modulated is caused to flow and has output electrodes connected in a series modulation circuit with a modulator tube having electrodes on which modulating potentials are impressed, both tubes being connected in series with a source of direct current potential to accomplish modulation of said wave energy by said modulating potentials, said modulator tube being in the high potential end of said series modulation circuit, means for impressing a direct current biasing potential on a controlling electrode of said modulator tube, an impedance for impressing an additional controlling potential on a controlling electrode of said modulator tube which varies in accordance with the modulations on said wave energy, and rectifying means coupling electrodes of said discharge tube to said impedance to impress thereon additional controlling potentials to control the bias of said modulator tube in accordance with the modulations on said wave energy.

ERNEST GREEN. 

